Hyperbranched Pyrenyl Poly(aryl piperidinium) Anion-Exchange Membrane and Its Application in Alkaline Water Electrolysis

Hyperbranched poly(terphenyl piperidine) with pyrene as the branched core is synthesized by co-polymerization of p-terphenyl, N-methyl-4-piperidone, and pyrene in the presence of acid. Anion exchange membranes (AEMs) with different degrees of branching are prepared by controlling the ratio of branching pyrene to backbone p-terphenyl. The chemical structure, thermal stability, mechanical feature, and ionic conductivity of the polymers are thoroughly studied. After casting, the AEMs are further applied into AEM water electrolyzers (AEMWEs) to evaluate their device performance under practical working conditions. The mechanical features and dimensional stability of AEMs have been improved by branching. The thermal stability of the AEMs is close to that of the linear control polymer-based membrane. The tensile strength of as-prepared AEMs reaches 73.5 MPa, which is 72% higher than the linear polymer-based membrane (42.8 MPa). The ionic conductivity of as-prepared AEMs reaches 78.2 mS/cm at room temperature and 168.0 mS/cm at 80 ℃. After branching, the water content (81.9% at 80 ℃) and swelling ratio (47.1% at 80 ℃) of as-prepared AEMs decrease significantly in comparison with linear control polymer-based AEM (water content: 139.2%, swelling ratio: 82.7%). In AEMWEs, the devices exhibit excellent electric current density of 1.95 A/cm² at 3 V and stable operation over 90 h.